Despite many significant advances in its prevention and management, infectious disease still accounts for considerable morbidity and mortality. The mechanisms by which mammals, including humans defend against microbial invasion are incompletely defined. Defensins are recently identified cysteine-rich, cationic peptides found in abundance in phagocytic leukocytes of several mammals. These peptides are responsible, in part, for the non-oxidative microbicidal activity of these cells toward microorganisms. Four defensins, all derived from granular leukocytes are known to exist in humans. In vitro, defensins have potent activity against bacteria, fungi and enveloped viruses. Recent studies in animal models have found that in addition to leukocytes, epithelial cells also express defensin-related molecules. Preliminary studies presented in this proposal show clear evidence of novel defensin gene expression in non-hematopoietic tissue of humans. Using a molecular biological approach, strong data have been obtained indicating that the family of human defensins is more diverse than currently appreciated, and some of these newly. discovered defensins are expressed exclusively in epithelial cells. The long range goal of this research is to define the role of epithelial defensins in host defense. Toward this goal the following experiments are proposed: 1) Clone and characterize genes corresponding to the non-hematopoietic defensins, establish the nucleotide sequence of selected genes and their flanking sequences, and determine a regional map of these genes which appear to be clustered; 2) Clone and characterize the cDNA encoding novel defensins and defensin-related peptide(s) from non-hematopoietic human tissues; 3) Characterize the cellular localization and antimicrobial properties of the newly discovered defensins; 4) Identify and characterize the cis-acting elements which regulate defensin expression. Epithelial-derived defensins are likely to equip mucosa] surfaces with a previously unrecognized defensive capability that complements other well-defined antimicrobial defenses. The understanding of the physiological regulation of epithelial defensins in humans may ultimately lead to therapeutic modulation of endogenous peptide expression, and may lead to the development of novel therapeutic antimicrobial peptides.